Microbial community succession in urban waterways following combined sewer overflow (CSO) discharge

Background/Question/Methods

Increasing population and aging sewage infrastructure in New York’s urban centers negatively influence coastal water quality while improved management and expanded recreational use challenge society to adopt a new vision for clean water in the region. Recent investment in wastewater treatment plant upgrades, especially in New York City (NYC), have resulted in significant improvements to bacterial water quality of the Hudson River Estuary. However, extensive Combined Sewer Overflow (CSO) (>25 billion gallons per year in NYC) discharge remains as a major input of allochthonous bacteria to waterways. It is the goal of this study to characterize the patterns of microbial community succession caused by CSO events in the Hudson River Estuary using a combination of cultivation and molecular genetic based assays. We hypothesize that CSO discharge will cause increased representation of enteric and antibiotic resistant organisms in surface waters following precipitation events and that the largest changes in community composition will occur in close proximity to CSOs. To test these hypotheses, the concentration of Fecal Indicator Bacteria (FIB) and Antibacterial Resistant Bacteria (ARB) were enumerated from time course sampling of urban surface water and CSO discharge.  In addition, bacterial community composition of surface water and CSO discharge were evaluated using large-scale 16S rRNA gene sequencing across weather conditions. 

Results/Conclusions

Measurement of fecal indicator bacteria from more than 3000 water samples in the Hudson River estuary demonstrate degradation of water quality that occurs with wet weather discharges.  For example, EPA beach action value guidelines for Enterococci concentration are exceeded in only 10% and 20% of samples from the waterways surrounding New York City and Albany, respectively, during dry weather but in 34% and 66% of samples following precipitation. Levels of FIB and ARB were found to be more than two orders of magnitude higher in CSO discharge during rain events than in adjacent surface water.  16S rRNA gene sequence analysis revealed >50 genera that were identified to be more than an order of magnitude more abundant in samples collected in close proximity to the CSO as compared to background surface water samples, with dominant CSO genera mostly enteric (e.g. Faecalibacterium, Blautia) or urban infrastructure (Acinetobacter, Arcobacter) associated. While monitoring programs routinely characterize the patterns of fecal indicator organisms to assess water quality degradation from sewage discharge, this study demonstrates the broader patterns of bacterial community succession caused by CSO discharge events on the urban waterways of New York.